Grid structure for electron tube



May 12, 1959 E. J. NAILL GRID STRUCTURE FOR ELECTRON TUBE 2'Sheets-Sheetl Filed Nov. 21, 1955 INVENTOR. EUGENE J. NAILL ATTORNEYS y12, 1959 E. J. NAILL 2,886,733

GRID STRUCTURE FOR ELECTRON TUBE Filed Nov. 21, 1955 2 Sheets-Sheet 2 {III In VIII/[1% 5 l &

INVENTOR.

EUGENE J. NAILL ATTORNEYS GRID STRUCTURE FOR ELECTRON TUBE Eugene J.Nail], New Canaan, Conn., assignor to Machlett Laboratories,Incorporated, Springdale, Conn., a corporation of ConnecticutApplication November 21, 1955, Serial No. 548,170

3 Claims. (Cl. 313-265) This invention relates to electrode structuresfor electron tubes and has particular reference to a novel gridstructure wherein a mesh grid is supported in a manner permitting freeexpansion of the grid with respect to its supporting structure whileretaining efiicient electrical contact therewith.

My copending application Serial No. 428,313 filed May 7, 1954, now U. S.Patent No. 2,850,664, shows and describes one method of improving uponknown prior grid structures, and the present invention is a furtherimprovement upon a similar electron tube structure.

In the presently described type of electron tube it is desirable toemploy a grid composed of a mesh of relatively fine interwoven wireswhich is positioned in pre determined close-spaced relation to andbetween a cathode and an anode for controlling flow of electrons fromthe cathode to the anode. The grid is preferably mounted upon one end ofa tubular support to which it is necessarily conductively connected.However, it is essential that the grid be permitted to freely expand,without breaking the electrical connection with the support, when itbecomes heated during operation of the tube.

The prior art shows various relatively ineffective ways of mounting meshgrids, but in most cases the grids are not permitted to expandsufficiently to prevent deformation such as produces variations in theinterelectrode spacings. In other cases, while the grids may expand, theelectrical conductivity between the grids and their supportingstructures is inefficient to such an extent that radio frequencycurrents are not efficiently passed through the structure.

Accordingly, it is a primary object of this invention to provide animproved grid structure for electron tubes wherein a mesh-type grid issupported upon and in efficient electrically conductive engagement witha generally tubular structure in desired spaced relation to an anode anda cathode, the grid being permitted to freely expand with respect to itssupporting structure without interfering with the electricalconductivity therebetween.

This objective is accomplished by providing a fiat annulus over the endof the tubular grid support, which annulus supports the marginal areasof the mesh grid. A flanged collar is positioned around thecircumference of the end portion of the support and the adjacent outerperiphery of the annulus, and the flange thereon engages the outerexposed surface of the grid. The collar is welded or otherwise secureddirectly to the support whereby efiicient electrical conductivity isassured between the support and the grid. The grid and annulus assembly,however, is not rigidly secured to the collar and thus is free to expandwhen heated.

Other objects and advantages of this invention will become apparent fromthe following description taken in connection with the accompanyingdrawings, wherein Fig. 1 is a front elevational view partly in axialsection illustrating a tube embodying a preferred form of thisinvention;

Fig. 2 is an enlarged axial sectional view of the grid structure of thetube shown in Fig. 1; and Fig. 3 is a plan view of the structure shownin Fig. 2. Referring more particularly to the drawings wherein likecharacters of reference designate like parts throughout the severalviews, the tube shown in Fig. 1 includes a glass cylinder 10 which formsa part of the tube envelope. To one end of the cylinder 10 isvacuum-sealed a tubular anode terminal 11 which supports within it ananode 12;

the active surface 13 of which is directed toward and in predeterminedspaced relation to the active surface of a cathode 14. The cathode 14 issubstantially planar and parallel to the active anode surface 13 and ismounted on one end of a tubular support 15 by which it is connected toone end of a tubular metal cylinder 16. The cylinder 16 is connected bya ring 17 of dielectrical material to a tubular terminal 18, the support15, cylinder 16, ring 17 and terminal 18 being substantially coaxial.

The terminal 18 supports therewithin a metal disc 19 to which isconnected one end of a filament-supporting rod 20. The rod 20 extendstoward the cathode 14 and has attached to it one end of a filament 21which is positioned adjacent the cathode 14 for heating purposes. Theother end of the filament 21 is connected by a conductor 22 to thecylinder 16. One end of a metal tube 23 is secured in encirclingrelation to the cylinder 16 and extends longitudinally of the device inspaced encircling relation to the first terminal 18. The outer endportion of the tube 23 is sealed to the inner surface of a secondtubular cathode terminal 24, thus providing; a complete circuit fromterminals 18 and 24 through the filament 21.

The outer terminal 24 is connected by a dielectric ring 25 to one end ofa coaxial cylinder 26 having its other end sealed to an intermediateportion of the inner surface of a coaxial tubular grid support 27. Theouter end portion of the grid support 27 is sealed to a tubular gridterminal 28 which is sealed to the adjacent end of the glass envelopeportion 10. The grid-support ing structure is thus coaxial with thecathode structure and anode. The inner end surface of the grid support27 terminates adjacent a plane passing between the anode and cathodesurfaces substantially perpendicular to the axis of the coaxialelectrodes.

On the inner end of the grid support 27 is positioned a metal annulus 29whichcarries a circular wiremesh grid 30, the grid spanning the centralopening in the annulus and having its marginal portions securely afiixedto the annulus by suitable means such as by brazing while the mesh ismaintained in stretched condition.

The annulus 29 having the grid 30 thereon is held in place on the end ofthe grid support 27 by a flanged collar 31 which fits over the support27 and annulus 29, with the flange portion 32 thereof overlying theouter surface of the grid 30. In assembling the device, the collar 31 isurged axially in the direction of the cathode terminals to press theflange portion 32 firmly against the grid 30, and then is spot-welded tothe support at frequent intervals around its circumference. This methodinsures efiicient conductivity between the support 27 and collar 31 aswell as between the collar 31 and grid 30.

The collar 31 is preferably made of a thin, soft metal which permits itto be welded to the support with light delicate Welds which do notdestroy the space relationships between the assembled parts such asmight result from distortion occurring during normal methods of welding.

It is particularly pointed out that with a thin collar 31, the collarmay be welded to the annulus 29 and the flange portion 32 thereof mayalso be welded to the grid, and when the grid and annulus are heatedduring operation of the tube the inherent characteristics of the IcePatented May 1 2, 1959 thin collar will permit flexing thereofsufficiently to allow relatively unrestricted thermal expansion of thegrid assembly.

Since the flange32 is annular in shape, it is apparent that asubstantially continuous annular line of contact is made between thegrid and flange insuring eflicient passage of radio frequency currents.While a continuous line of contact is not required for eflicientoperation of a tube, it is preferred that the area of contact around thegrid be substantially continuous, and at least of greator area than thatwhich is provided by spaced contacts.

With the present construction it is also apparent that the supportingstructure for the grid does not require the use of movable memberswhich, in order to function efliciently, must be inherently relativelythin and flexible. The grid 30 of the present invention is permitted,with the annulus 29, to expand freely. The flange does not provide anyamount of restriction such as would prevent the desired free expansioncharacteristics and does provide means for obtaining the desired areacontact for efficient radio frequency current conductivity.

A further desirable feature of a coaxial tube structure as describedlies in the fact that the end of the cylinder 27 may be presented,during assembly of the tube, as a locating surface for the grid. Thisparticular construction permits the end surface of the cylinder 27 to bemachined so as to be parallel with and in exact spaced relation to theactive surface of the cathode, which desirable method of fabricationcannot readily be performed in other tube structures.

From the foregoing description it is apparent that an improved gridstructure for electron tubes has been provided in accordance with theobjects of this invention. It is also apparent that variousmodifications Within the scope of the invention may occur to thoseskilled in the art. Therefore, it is to be understood that the detailsof construction described herein shall be interpreted as illustrativeand not in a limiting sense.

I claim:

1. An electrode structure for an electron tube, comprising a rigidannular support, an electrode having thermal expansion characteristicspositioned on the rigid support and consisting of an annulus having agrid affixed thereto and spanning the central opening therein, and acollar affixed in encircling relation to the support and freelyencircling the outer periphery of the electrode, said collar having aflange engaging the exposed surface of the electrode and retaining theelectrode firmly upon the support, said flange being characterized byits ability to flex with changes in thermal expansion characteristics ofthe eleo trode.

2. An electrode structure for an electron tube, comprising a rigidsubstantially tubular support having one end provided with a continuousplanar annular surface, an electrode having thermal expansioncharacteristics positioned on the annular end of the rigid support andconsisting of a relatively flat annulus having one side surface engagingsaid end of the support and having a circular mesh-type grid afiixedthroughout its marginal area to the other side of the annulus andspanning the central opening therein, and retaining means conductivelyconnecting the grid with the rigid support and retaining the electrodefirmly upon the annular end thereof comprising a ring encircling the endof the support and the outer periphery of the electrode, the ring beingaffixed to the support and having an inwardly turned flange overlyingthe electrode and in firm conductive engagement with the marginalportion of the grid, the flange being relatively thin and capable ofrelatively easily flexing under the influence of changing thermalexpansion characteristics of the electrode.

3. In an electron tube embodying an envelope containing substantiallyplanar cathode and anode electrodes having their effective surfaces inspaced substantially coaxial parallel relation, a grid electrode havingthermal expansion characteristics positioned between the effectivesurfaces of the cathode and anode electrodes and comprising a wire meshgrid aflixed throughout its marginal area to one side of a relativelyflat annulus, a relatively rigid annular support encircling the cathodeelectrode and engaging and supporting the annulus, and a collarconductively connecting the grid with the support and retaining the gridelectrode firmly upon the support, the collar being aflixed to theperiphery of the support and having an inwardly turned flange overlyingand in firm conductive engagement with the marginal portion of the grid,the flange being relatively thin and capable of relatively easilyflexing under the influence of changing thermal expansioncharacteristics of the grid electrode.

References Cited in the file of this patent UNITED STATES PATENTS2,446,271 Eitel Aug. 3, 1948 2,455,868 Koch Dec. 7, 1948 2,467,303Watson Feb. 8, 1949' 2,714,676 Machlett et al Aug. 2, 1955

